Star Trek creator Gene Roddenberry derived the name Klingon from his past as a police officer. Roddenberry created Star Trek in 1964 with its original pilot, "The Cage," which was rejected by NBC. Before he was a successful television producer, Roddenberry was a sergeant in the Los Angeles Police Department, and Gene drew inspiration from his life when developing ideas for Star Trek.
https://screenrant.com/star-trek-gene-roddenberry-klingon-name-origin/